Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle plate. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved across the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
One particular example of a prior art inkjet print cartridge is shown in FIG. 1a as print cartridge 10. Print cartridge 10 includes an ink reservoir 12 for containing liquid ink. The liquid ink is delivered to a printhead 14, and resistors within the printhead 14 are selectively energized to vaporize a small portion of ink, which is then expelled through an associated orifice, such as orifice 16. Orifices 16 are formed in a nozzle plate 18, typically formed of nickel, which is secured over a substrate containing the resistors.
To provide current to each of the resistors, conductors within a flexible circuit 22 are connected to the appropriate electrodes on the substrate. These conductors are terminated by contact pads 23 exposed on the surface of flexible circuit 22. When cartridge 10 is properly positioned in an inkjet printer, contact pads 23 are pressed against associated contacts on the inkjet printer so as to electrically couple the resistors to a source of electrical current.
A close-up view within the circled portion 1b in FIG. 1a is shown in FIG. 1b. FIG. 1b shows more detail of nozzle plate 18 incorporating orifices 16 and additionally shows conductors 24 formed on the underside of flexible circuit 22.
Also illustrated in FIG. 1b is a barrier layer 26, which separates nozzle plate 18 and a substrate 28, wherein barrier layer 26 provides the ink manifold and vaporization chambers into which ink flows from ink reservoir 12 for vaporization by the energized resistors formed on substrate 28.
FIG. 1c illustrates printhead 14 removed from print cartridge 10. FIG. 1c shows nozzle plate 18 partially cut away to reveal the pattern formed in barrier layer 26. Substrate 28 is shown having thin film resistors 30 formed thereon and also having metal electrodes, such as electrode 32, formed thereon connected to each of resistors 30. Conductors 24 (FIG. 1b) are aligned with electrodes 32 and permanently secured to electrodes 32 using automated bonding or tacking equipment, such as a TAB bonder.
Ink flows from the back of substrate 28 through a center slot 34 and into each of the vaporization chambers 36. When a resistor 30 is energized and thus heated, the ink within a vaporization chamber 36 is vaporized and is expelled through an associated orifice 16 formed in nozzle plate 18.
FIG. 1d is a cross-section of a vaporization chamber 36 taken along line A--A in FIG. 1c. Shown in FIG. 1d is substrate 28, barrier layer 26, nozzle plate 18, resistor 30, orifice 16, vaporization chamber 36, expelled ink droplet 38, and recording medium 40. In operation, ink fills vaporization chamber 36, and resistor 30 is energized. The ink within vaporization chamber 36 is evaporated and expelled as droplet 38 through ink orifice 16. Expelled droplet 38 then forms a dot on the recording medium 40.
The print cartridge structure 10 shown in FIGS. 1a and 1b has a number of drawbacks. Since this disclosure is directed to an improved insulation system for preventing ink shorting of conductors, only the drawbacks relating to the shorting together of conductors 24 by ink will be discussed.
As illustrated in FIGS. 1b and 1c, conductors 24 extend out from flexible circuit 22 and connect to electrodes 32 on substrate 28. There is no insulation on the bottom surface of conductors 24 formed on the bottom surface of flexible circuit 22. During the course of printing, cleaning operations need to be done to prevent nozzles 16 from clogging. In addition spray from the ink ejection is generated. As a result, the ink manages to reach the underside of flexible circuit 22, which causes some degree of shorting between conductors 24. At low voltage levels and at fairly low operating speeds, this shorting together of conductors 24 only moderately affects the operation of printhead 14. However, future generation of printheads will require faster and faster speeds and possibly incorporate active demultiplexing circuitry on the printhead itself. Thus, high current power supply voltages and low current control signals will be carried by conductors connected to future printheads. Ink shorting between these conductors will significantly affect the characteristics of the control signals and will, therefore, cause significant fluctuations in print quality.
Accordingly, what is needed is a structure for preventing any shorting by ink between conductors leading to electrodes on a printhead substrate.